Feasibility analysis of a movable bridge compensating for clearance deficit during floods

This paper deals with the problem of mountain river crossing in old towns whose urban morphology often prevents one from building a ramp to access the bridge. If this is the case, the proposed solution consists in designing a bridge which can be lifted when a flood occurs. Some bridges of this kind are actually on duty in the Italian Alps but all of them are moved by means of hydraulic jacks. A table bridge moved by the buoyancy force of the river water is suggested. The design concept is here specified for a real case where a floating bridge is placed in the position where a bridge moved by hydraulic jacks was built. This choice enables one to compare the two solutions under the same conditions. The simplicity and robustness of the design, as well as the possibility of fully automatic functioning without any external support (i.e. electric energy) lead the authors to state that the floating bridge suggested is preferable to a bridge lifted by means of hydraulic jacks.